Apparatus for measuring electrical resistances.



, PATENTED MAR. 24, 1903.

R. W. CONANT. APPARATUS FOR MEASURING ELECTRICAL RESISTANOES.

APPLICATION gum) SIEPT. 29, 1902.

2 SHEETS-SHEET 1.

H0 MODEL zf f co.. PHOYO-LITND wrsumemm 0. 3

No. 723,369. PATENTED MAR..2,4, 1903.

' R. W. UONANT.

APPARATUS FOR MEASURING ELECTRICAL RESISTANGES. 1

APPLICATION FILED SEPT. 29. 1902. R0 MODEL. 2 SHEETS-SHEET 2.

I 5 m i Wit/36.51929 .5.

UNITED STATES PATENT OFFICE.

ROGER CONANT, OF CAMBRIDGE, MASSACHUSETTS.

APPARATUS FOR MEASURING ELECTRICAL RESISTANCES SPECIFICATION formingpart of Letters Patent No. 723,369, dated March 24, 1903.

- Application filed September 29, 1902. Serial No. 125,176. (No model.)

T at whom it may concern:

Be it known that I, ROGER W. OoNAN'r, a citizen of the United States,residing in Cambridge, in the county of Middlesex and State ofMassachusetts, have invented an-Improvement in Apparatus forMeasuringElectrical Resistances, of which the following description, inconnection with the accompanying drawings, is a specification, likecharacters on the drawings representing like parts.

This invention relates to an apparatus for rapidly and eflicientlymeasuring electrical resistances, and is especially applicable formeasuring the resistance of rail-joints in the tracks ofelectric-railway systems.

The present invention is an improvement upon the invention shown anddescribed in United States Letters Patent N 0. 645,384,

granted to me March 13, 1900, and has for one of its objects to providea testing apparatus which can be worked by a single operator.

Another feature of the present invention consists in providing a novelcontact device,.

as will be described, whereby a more efficient connection with the railsof the track may be obtained.

These and other features of this invention will be pointed out in theclaims at the end of this specification.

Figure 1 is a perspective view of a box or case forming part of anapparatus embodying this invention; Fig. 2, a front elevation of the boxor case shown in Fig. l with its cover raised and its front sidepartially broken away; Fig. 3, a plan view of the box or case with itscover removed; Fig. 4, a diagram of circuits illustrating the operationof the invention and including in elevation a portion of two rails andmy improved contact device, and Fig. 5 a diagram of circuitsillustrating a modification to be referred to.

The main portion of the apparatus herein shown as'embodying thisinvention is substantially such as shown and described in the patentreferred to. It consists, essentially, of the box or case a, providedwith the cover I) and strap 0, and the terminal plates d e on the cover17, with which cooperates the switch-1ever f, which is adapted to makecontact with either terminal or to bridge them. The case orbox isprovided with the binding-posts i j and with the lever m and circuitterminal or ed on the insulatingblock 13. 'The clock mechanism isadapted to be wound by the key 14, and the break-wheel is held at restby the spring-arm 15, which engages the shaft or pivot of theescapement-fan 16. The springarm 15 has extended through it the pivot 17for the lever m and is adapted to be disengaged from the shaft of theescapement-fan when the lever m is thrown over onto the terminal button11., which latter forces the lever m outward and draws the spring-arm 15away from the escapement-shaft 16. The terminal pen or brush 12 and theswitch m are included in circuit with the telephone 3, the pen 12 beingconnected with the binding-postj by the p, and the binding-post 0 isconnected by wires 31, 32, and 33 to the terminal a. The

wire 24 is connected by wire 26, coil 29, and

wire 30 to the wire 31, The binding-posts 1} j k are adapted to haveconnected-to them the flexible conductors 40 41 42, connected withportable circuit-terminals 43 44 45. The circuit-terminals 43 44 45 inaccordance with one feature of this invention are adapted to bemechanically connected together, so as to form one piece of apparatus,which may for "sake of convenience be termed a tripartite portablecontact apparatus, which may be made as herein shown.

Referring to Fig. 4, the contact apparatus referred to consists of acenter pole 50, of wood or other suitable material, provided with asteel chisel forming the center contact member or terminal 44, to whichare secured,

or angle-irons 53 54, having suitably attached to them two extensionbeams or spring-arms 56 57, of wood or other suitable material, whichcarry at their free ends the two terminals 43 45, preferablychisel-shaped and arranged with their cutting edge substantially atright angles to the cutting edge of the center terminal 44 and extendedin the direction of the length of the rails 60 61, with which they aredesigned to make contact and which form a part of the return for theelectric-railway system. The extension beams or arms 56 57 are securedto the center pole a distance from its end or point sufficient to causethe center contact or terminal to be elevated above the rail, preferablyabout one inch, when the outer terminals or contact-points are inengagement with the rails. The center terminal is brought in contactwith the rail by pressure applied by the foot of the operator to one ofthe extension beams or arms near the center pole. hen pressure is thusapplied to the extension-beam, it will be seen that the beam or arm isdepressed or sprung downward and the outer ends of the beams are causedto move longitudinally of the rails, thereby moving the outer terminalsalong the rails and causing their sharp edges to cut into the rails andmake a perfect contact therewith. This cutting effect of the outsideterminals may be intensified or increased by moving the upper end of thecenter pole 50 back and forth, while its chisel-point is held in firmcontact with the rail and acts asa fulcrum for the elbow-levers formedby the center pole and the extension-beams. The rocking movementreferred to enables the end chisels to cut through the hard scale on therail produced by the rolling action of the carwheels and does notdisturb the contact of the center chisel. The chisel-shaped terminalsare preferably made of the best quality and temper of steel. It will benoticed that the extension-beams can be quickly and easily detached fromor attached to the center pole by the single thumb-screw 52, therebyenabling, the three parts of the contact apparatus to be gatheredtogether and easily carried.

Within the box or case a is a rheostat or resistance 630, which, asshown in Fig. 4, has one end connected by the wire 21 with thebinding-post 7c and its other end connected by wire 63 with thebinding-post j through the wire 20. The resistance 630 is provided witha series of points or buttons with which cooperate a switch-lever 64,which is connected to the terminal plate (Z through a resistance 65. Theresistance 630 is graduated and its points have a fixed ratio with theother side of the instrument-that is, with a standard resistance-whichin the present case is the length of rail between the chisels orterminals 43 44, which length for convenience may be three feet. In Fig.4 the ratio referred to is represented as one, 1.5, two, three, four,six, eight, fifteen, thirty, ninety. The purpose of the rheostat 630 istoenable the operator to make the opposing drops of potential equal onboth sides of the instrument, which fact is manifested at the telephoneby the absence of sound, or it may be manifested in a galvauometer orlike instrument 66 (see Fig. 5) by the position of the needle thereof.The binding-post t'is connected to the terminal plate e by the wire 22,which includes the resistance 67.

The operation of the apparatus may be readily understood from thediagram shown in Fig. 4. The operator places the tripartite contactapparatus upon the rails with the center terminal 44 and the outerterminal 45 substantially equidistant on opposite sides of the railjoint 68. He then applies his foot to the beam or arm 57 and brings thecenter terminal into firm contact with the rail 60, and, if desired, hethen rocks the pole back and forth, as indicated by dotted lines,thereby obtaining a most efficientcontact of the terminals 43 45 withthe rails 60 61. The switchleverf is placed in its central positionbridg ing the terminals (1 e, and the circuit-breaker is then set inoperation by moving the lever on onto the terminal button a. Theoperatorthen moves the rheostat-lever 64 from the first point at which a roaringor loud sound is heard in the telephone to the point on the scale atwhich the sound in the telephone is diminished appreciably and isweakest or no sound is heard. The current for the telephone is suppliedfrom the rails 60 61 and is due to the drop in potential of the currentflowing through the rails. The current flowing through the rails may bethe return-current of the system when the latter is in use; but the saidcurrent can be supplied to the rails from a source extraneous to that ofthe railway system, if so desired. In other words, the operator afterstarting the circuit-breaker in operation moves the rheostat-lever overthe resistance-points until he obtains silence in the telephone. Forexample, if the lever is moved to the point 2 and no sound is heard atthe telephone then the resistance of the rail-joint 68 is equal totwicethe three feet mentioned above, or six feet of rail. If the position ofsilence is obtained between two of the contact-points, then theresistance is obtained by multiplying the indication on the scale by thethree feet of standard lengthas, for instance, when the rheostat-leveris between the points 3 and 4 and no sound is heard in the patent abovereferred to-namely, by moving the two-way switch f onto the terminalplate (1, with the rheostat-switch on its first point. The telephone isthen in circuit simply with the rail-joint, and this sound becomeslouder and louder the higher the railjoint resistance. NVhen the two-wayswitch fis thrown onto the terminal e, the sound at the telephone isproduced from the standard length of rail included between the centerpoint or chisel 44 and the outer chisel 43, which is the standardlength--namely, three feet in the present instance. With the twowayswitch in its middle position the railjoint is opposed to the sound ofthe standard length of rail and if equal to it kills it, so that thereis silence in the telephone. As the rail-joint is usually the louder,the purpose of the rheostat is to enable a determination to be madesubstantially in an instant of how much greater is the sound from therail-joint than from the three feet of rail. This is accomplished withthe two-way switch in its middle position by moving the rheostatswitchover its points, which cuts down the joint-sound until it is equal tothe rail-sound, thereby killing it. When this condition is obtained, allthat is necessary for the operator to do is to multiply the number onthe scale at which the rheostat-switch is stopped by three.

While I prefer to employ the telephone and the circuit-breaker inconnection with the rheostat and tripartite contact apparatus hereinshown, I do not desire'to limit myinvention in this respect, as therheostat and the tripartite contact apparatus can be used to advantagewith other forms of indicating instrumentas, for instance, instead ofthe telephone and the circuit-breaker and kicking-coil I may employ oneor more galvanometers or other meters 66, as indicated in Fig. 5--theadvantage to this form of instrument being that it is rendered moreefficient by reason of the fact that the readings are rendered easier totake with the fluctuating currents ordinarilyexisting in the rails, and,further, a superior contact is obtained with the tripartite contactapparatus.

In the diagram Fig. 4 I have shown a duplicate break-wheel and motormechanism, which in practice may be secured to the partition-wall 2 andlocated in the compartment 5 ready for use in case of accident to themotor mechanism for the break-wheel in compartment 8.

I prefer to use the kicking or self-inductive coil 29, as itconcentrates the available energy on the break in the telephonecircuit,and practically no sound is obtained on the make.

I claim- 1. In an apparatus of the character described, the combinationwith two independent metallic circuits having a conductor com- 7 mon toboth, a source of current for said circuits, a telephone-receiver in thecommon conductor, a rheostat having its resistance-coils connected withone side of one circuit and with the common conductor around or in shuntwith the telephone-receiver, and a rheostat-switch cooperating with saidcoils.

2. In an apparatus of the character described, a tripartite contactapparatus comprising a pole or upright, a center contact member orterminal, spring-arms extended in opposite directions from the saidcenter contact member and provided with contactterminals near theirouter end, substantially as described.

3. In an apparatus of the character described, a tripartite contactapparatus comprising a center contact member or terminal, spring-armsextended in opposite directions from the said center contact member andprovided with contact-terminals having their cutting edges extendedsubstantially at right angles to the cutting edge of the centercontact-terminal, substantially as described.

4. An apparatus for measuring electrical resistances, comprisingportable terminals adapted to engage the resistance to be measured andto engage a standard resistance, an indicating instrument in circuitwith said terminals, and a rheostat having its resistancecoils connectedin series with the resistance to be measured, and its switch in serieswith said indicating instrument and cooperating with said resistance-coils to substantially equalize the opposing drops of potential on bothsides of the instrument, substantially as described.

5. An apparatus for measuring the electrical resistance of rail-joints,comprising contact-terminals adapted to engage thejrails, an indicatinginstrument in circuit with said terminals, and means in circuit with theindicating instrument and with the rail-joint for substantiallyequalizing the drop of potential of a standard length of rail with aportion of the drop of potential in the rail-joint, substantially as andfor the purpose specified.

6. An apparatus for measuring electrical resistances, comprising atripartite contact apparatus having two of its contact-terminals inengagement with a known resistance and the other of saidcontact-terminals with the unknown resistance, an indicating instrumentin circuit with the said terminals, and a rheostat in circuit with theindicating in- I strument, substantially as and for the purposespecified.

In testimony whereof I have signed my name to this specification in thepresence of two subscribing witnesses.

ROGER W. C ONANT.

Witnesses:

J AS. H. CHURCHILL, J. MURPHY.

